The present invention relates to the reduction of the oscillation threshold value of a semiconductor laser.
Ordinary semiconductor lasers often employ a double hetero-structure, that is, such a structure that an active layer, which contributes to light emission, is sandwiched between semiconductor layers of larger energy gap and lower refractive index than those of the active layer. This is intended to aim at the effect of reducing the oscillation threshold value by confining both injected carriers and light to the vicinity of the active layer to thereby promote the interaction of guided light and the carriers. However, conventional semiconductor lasers have defects, such as overflowing of injected carriers over the hetero barries and very complex control for crystal growth.